Our previous studies have demonstrated a bactericidal activity for human lactoferrin against a variety of oral microorganisms. The overall objectives of this proposal are to characterize the mechanism(s) of this bactericidal action and to determine potential interactions of lactoferrin with other salivary immune factors in the regulation of the oral microbial flora. The influence of cell surface components on the action of lactoferrin will be determined by studying (a) the susceptibility to lactoferrin of mutants defective in cell wall structure and organisms grown under conditions which modify the cell wall; (b) the potential for competitive inhibitions of lactoferrin by isolated cell wall components; (c) the effect of chemical modification of the bacterial cell surface on lactoferrin interaction. The influence of lactoferrin on membranes; including conformational changes transport and leakage will be studied. The effects of lactoferrin on cell metabolism, including stored energy potentials and levels of glycolytic intermediates, will be determined. The initial kinetics of lactoferrin shutdown of macromolecular synthesis and the effects of lactoferrin on the degradation of DNA, RNA and proteins will be determined. Lactoferrin will be physically and chemically modified to characterize potential sites and conformational slates involved in its bactericidal activity. Interactions between lactoferrin and other salivary proteins will be studied. The biological activity and interaction of plaque bound lactoferrin, lysozyme, lactoperoxidase and salivary antibody will be assessed by measuring metabolic parameters of microorganisms in the plaque matrix and comparing this with pure cultures of plaque isolate. The mechanism(s) of lactoferrin killing will be compared with that of conalbumin and transferrin.